Sum up what the text said about the radar system.

1. Read the new words:

to combine соединяться, объединять(ся)

unit устройство; узел; блок; прибор;

toemit излучать, испускать, выделять

electromagnetic energy электромагнитная энергия, энергия электромагнитного поля

to bounce back отскакивать назад

Doppler effect эффект Доплера, доплеровский эффект, доплеровская частота

Doppler shift доплеровский сдвиг (частоты)

sound wave звуковая волна

oscillation колебания, осцилляция, вибрация , генерация

wave pattern волновая картина, волновой спектр

to mirror отражать, показывать

segment доля, часть; составная часть

peakвысшая точка, пик, амплитуда

valley точка минимума, понижение

speeder водитель, превышающий разрешенную правилами движения скорость

2. Read the text and translate it:

A basic speed gun is just a radio transmitter and receiver combined into one unit.

The simplest function of radar is to tell you how far away an object is. To do this, the radar device emits a concentrated radio wave and listens for any echo. If there is an object in the path of the radio wave, it will reflect some of the electromagnetic energy, and the radio wave will bounce back to the radar device. Radio waves move through the air at a constant speed (the speed of light), so the radar device can calculate how far away the object is based on how long it takes the radio signal to return.

Radar can also be used to measure the speed of an object, due to a phenomenon called Doppler shift. Like sound waves, radio waves have a certain frequency, the number of oscillations per unit of time. When the radar gun and the car are both standing still, the echo will have the same wave frequency as the original signal. Each part of the signal is reflected when it reaches the car, mirroring the original signal exactly.

But when the car is moving, each part of the radio signal is reflected at a different point in space, which changes the wave pattern. When the car is moving away from the radar gun, the second segment of the signal has to travel a greater distance to reach the car than the first segment of the signal. If the car is moving toward the radar gun, the second segment of the wave travels a shorter distance than the first segment before being reflected. As a result, the peaks and valleys of the wave get squeezed together: The frequency increases.

Based on how much the frequency changes, a radar gun can calculate how quickly a car is moving toward it or away from it. If the radar gun is used inside a moving police car, its own movement must also be factored in.

Police officers have been catching speeders this way for more than 50 years. Recently, many police departments have added a new sort of speed detector, one that uses light instead of radio waves, also called a lidar gun (for light detection and ranging).

3. Answer the following questions:

1) Can radar be used to measure the speed of an object.

2) What will happen if the radar gun and the car are standing still.

3) What can be observed when the car is moving.

4) Is there any difference in the signal motion when the car is moving either away from the radar gun or toward the gun.

5) Is a radar gun based on how much the frequency changes?

6) Policemen have been using conventional radar guns since the 1950’s, haven’t they?

7) What a new sort of speed detector do you know?